1. Field of the Invention
The present invention relates to a vector quantization image processing apparatus for coding video signals with a high efficiency.
2. Description of the Prior Art
In supporting the present society, there has been enhanced importance held by information. To cope with this trend, the needs for the electronic communication services have been elevated and diversified. As one of these diversified services, there is a scheme to incorporate image services in addition to the existing music and sound services.
However, in general, image information involves a large amount of information to be generated and a large surplus degree. For this reason, it is necessary for the amount of information to be curtailed by high efficiency encoding. In realizing this high efficiency encoding, vector quantization is being studied.
Conventional vector quantization image processing apparatuses include a mean value separation circuit, an amplitude normalization circuit, a distortion operation circuit, a codebook ROM, and a distortion detection circuit. The mean value separation circuit takes in an input vector which is constituted by converting image data into a block form, and it calculates the mean value of the amplitudes of all elements of the inputted vectors to output the obtained mean value, and also outputs the vector with a zero mean after subtraction of the mean value from the amplitude of each element of the inputted vector. The amplitude normalization circuit calculates a standard deviation from the vector with a zero mean from the zero mean circuit as an amplitude coefficient to output the obtained amplitude coefficient, and also outputs the vector with a zero mean and unit standard deviation obtained by subtracting the amplitude coefficient from each element of the inputted vector. The distortion operation circuit is so operated that, when a vector with a zero mean and unit standard deviation is sent, it reads out the output vectors sequentially from the codebook ROM (Read Only Memory), and calculates the total of the absolute values of the differences of each element between the vector with a zero means and unit standard deviation and the output vector as a distortion, and it outputs, of the output vectors stored in the codebook ROM, an index value corresponding to the output vector whose distortion with the vector with a zero mean and unit standard deviation was the smallest. (Ref.: "Vector quantizer of video signals "Electron, Lett., Vol. 7, pp 1005-1006 November 1982).
Such a conventional vector quantization image processing apparatus shows an effect of eliminating the statistical property of the image by separating a zero mean from the input vector and dividing it by the unit standard deviation, but has a defect in that it requires a long operation processing time period.